Electromagnetic pickup with exchangeable stylus assembly for phonograph records



l 4 7 t B 4 m 3 S 8 y 3 t 3w e h T S S 3 ms BD W. KRIEBEL ET ALELECTROMAGNETIC PICKUP WITH EXCHANGEA ASSEMBLY FOR PHONOGRAPH RECOR 8 w6 .d m 4 c. 1 m y d a m l PIP/O FA/PT M 1 ns 0, X N Wu 1 May 14, 1968KRlEBEL AL 3,383,474

ELECTROMAGNETIC PICKUP WITH H EABLE STYLUS ASSEMBLY FOR PHONOGRAPH CORDSFiled Dec. 21, 1964 5 Sheets-Sheet 2 7 FIG? F/GIJ May 14, 1968 w,KRlEBEL ET AL 3,383,474 ELECTROMAGNETIC PICKUP WITH EXCHANGEABLE STYLUSASSEMBLY FOR PHONOGRAPH RECORDS Filed Dec. 21, 1964 3 Sheets-Sheet 5United States Patent 3,383,474 ELECTROMAGNETIC MCKUP WITH EXCHANGE- ABLESTYLUS ASSEMBLY FOR PHONUGRAPH RECORDS Walter Krieoel, Kiel, and GustavMans, Eutin, Germany,

assignors to Electroacustic Gesellsehaft mit beschrankter Haftuug, Kiel,Germany, a corporation of Germany Filed Dec. 21, 1964, Ser. No. 419,801Claims priority, application Germany, Dec. 23, 1963, E 26,098 22 Claims.(Cl. 179l00.41)

ABSTRACT OF THE DISCLGSURE The magnetic circuit of an electromagneticpickup for phonograph records has at least one pair of pole shoes spacedfrom each other to form a pole gap. An armature is positioned in the gapextending in length substantially parallel to and spaced from the poleshoes and has a length which is less than that of any of the pole shoes.Each of the pole shoes is subdivided into a fixed portion and aremovable end portion at the gap and the removable end portion of eachengages the corresponding fixed portion and protrudes therefrom. Anexchangeable assembly comprises an armature and a stylus carrier securedto the armature and extending colinearly therewith. Each of theremovable pole shoe portions is part of the exchangeable assembly andforms, When engaging one of the respective fixed portions and conjointlytherewith, an intermediate space between the removable end portion andthe corresponding fixed portion laterally of and extending to andopening on the armature. Two opposite ones of the spaces have conjointlywith the pole gap a larger width than the pole gap only. An elasticbearing member surrounds the armature and is mounted in the spaces.

Our invention relates to electromagnetic pickups for reproduction ofmonophonic or stereophonic phontograph records. More particularly, theinvention concerns itself with pickups whose stylus carrier is fastenedto a magnetizable or permanent-magnetic armature which is vibratorilymounted between pole shoes of a magnet system equipped with coil meansfor generating or varying electric voltages in accordance with theundulations of the record grooves engaged by the stylus. Pickups of thiskind are known, for example, from US. Patents 3,077,521 and 3,077,522.

For optimal reproduction quality, the tracking force and the equivalentmass at the stylus tip should be minimal and the compliance should be ashigh as feasible. This requires minimizing the counteracting inertiamoments and return forces of the pickup system, and thus leads toextremely small geometric dimensions, for example, elastic bearingshaving a thickness of but a few tenths of one millimeter. The resultingdifiiculties in construction and assembly work are aggravated by therequirement that the stylus member be easily exchangeable withoutjeopardizing the high quality of reproduction achieved by the extremelysmall dimensions and very low weight. If exchanging the stylus member istoo difiicult, it is usually neglected, thus defeating all otherexpedients toward highquality reproduction because the worn stylus tipis no longer capable of following fine details of the recordings andcauses permanent damage to the record grooves.

It is therefore an object of our invention to facilitate the manufactureand especially the assembly of those parts in an electromagneticphotograph pickup that are responsible for high-quality reproduction,and to satisfy the mutually contradictory requirements toward furtherimprovement of reproduction quality, on the one hand, and

greater ease of exchangeability of the stylus assembly by laymen, on theother hand.

To this end, and in accordance with a feature of our invention, eachpole shoe 0f the electromagnetic system is subidivided into a fixedportion and a removable end portion, both forming jointly a member of atleast one pair of poles with an intermediate pole gap in which thearmature is vibratorily mounted; and the removable pole-shoe portions,as well as the armature and its bearing member, constitute part of theexchangeable assembly, thus being removable from and attachable to, thefixed portion of the electromagnetic system together with the stylussystem. When the exchangeable assembly is attached, the removablepole-shoe portions are seated on the respective fixed pole-shoe portionsand form around the armature a cavity whose width is larger than that ofthe field gap. The elastic bearing member, such as a rubber grommet, isseated in this cavity and is firmly joined with the armature.

As a result, assembling and exchanging the stylus system is considerablyfacilitated and various further improvements in reproduction quality areafforded. Especially the critical dimensions of the armature hearing maybe given an easily manipulatable order of magnitude of a fewmillimeters, in contrast to the conventional, difficile dimensions of afew tenths of one millimeter. Nevertheless, the oscillating parts of thepickup system may retain the necessary small dimensions. Indeed, byvirtue of the invention, the dimensions of these other components may befurther reduced for further improved reproduction quality. Furthermore,the air gap between pole shoe and armature is no longer determined bythe slightest geometric dimensions of the elastic bearing member required for sufficient elasticity, but may now be chosen independently ofthe desired elasticity and only in accordance with the required oroptimal armature travel, even in cases where the particular design ofthe pickup requires mounting the elastic bearing member within the airgap. This, in turn, affords obtaining a higher signal voltage andthereby a more favorable signal-to-noise ratio, or it permits furtherreducing the size of the armature, both also contributing to betterreproduction qualities.

According to another, preferred feature of our invention, theexchangeable portions of the pole shoes are rigidly joined mechanicallybut magnetically isolated from each other so as to form a mechanicalunit which contains a cavity, merging with the above-mentioned poleshoecavities to form a single large hollow space. The elastic bearing memberis additionally or exclusively mounted and supported in this commonhollow space within the exchangeable unit.

By virtue of the invention, the elastic bearing member may be given amore readily manipulatable and exchangeable shape as compared with theminute grommets heretofore used as best suitable. The movable pole-shoeportions and the elastic bearing member can be more readily and moreaccurately mounted, and they reliably retain during exchange theaccurate positions required for optimal cooperation with the fixedpole-shoe portions and the armature. This also secures and reliablypreserves an accurately defined working position of the armaturerelative to the pole shoes.

According to still another feature of the invention, the elastic bearingmember is predominantly braced against the wall portions of the cavityspace which are most remote from the armature. This permits giving thebearing a low elastic return force yet a handy shape which facilitatesassembling.

The above-mentioned and further objects, advantages and features of ourinvention, said features being set forth with particularity in theclaims annexed hereto, will be apparcnt from, and will be described in,the following with reference to embodiments of pickups according to theinvention illustrated by way of example in the accompanying drawings,wherein:

FIG. 1 shows schematically and in perspective a known pickup for thepurpose of explanation with reference to the embodiments of theinvention shown in the other illustrations.

FIG. 2 is a longitudinal section through part of a pickup according tothe invention.

FIG. 3 is a cross section along the line A-B of FIG. 2, but rotated 45to make the pickup suitable for stereo phonic recordings.

FIG. 4 shows in section another embodiment according to the invention.

FIG. 5 is a perspective view of a mounting unit which forms part of thepickup shown in FIG. 4.

FIG. 6 shows perspectively and in exploded fashion a detail of FIGS. 4and 5.

FIGS. 7, 8 and 9 show three additional embodiments differing withrespect to the spearation between the poleshoe portions and theformation of an intermediate space seating the elastic bearing member.

While the embodiments of the invention described hereinafter will beexplained with reference to the known and commercially available pickupsystem whose essential parts are shown in FIG. 1, it should beunderstood that the invention is not limited thereto.

The pickup according to FIG. 1 has a stylus tip 1 of sapphire or diamondmounted on a carrier 2 of non-magnetic metal such as aluminum, which isrigidly fastened to a prismatic and longitudinally magnetized armature 3of permanent-magnet material. The parts 1, 2 and 3 thus form a stylussystem which is vibratorily mounted within a non-magnetic sleeve 4. Theinterspace between armature and sleeve is largely filled with elasticmaterial 5, such as a sleeve or grommet of synthetic rubber, by virtueof which the armature 3 can pivot toward all sides relative to thesleeve 4. The sleeve 4 is exchangeably positioned between pole shoes 6.Illustrated are four such pole shoes of which each two opposite onesform a pair appertaining to a magnetic circuit and 90 displaced from theother pair. The magnetic circuits 7 carry respective windings 7' inwhich voltages are induced when the armature 3 performs pivotaloscillations, being deflected by the stylus tip 1 travelling in a recordgroove. The axis of the tip 1 must be directed at an angle of 45relative to the gap direction of each pole-shoe pair for reproducingstereophonic recordings.

The operation of the pickup involves the known dynamoelectric principle.When the stylus tip 1 is deflected by the undulations of a recordgroove, the resulting pivotal movements of the armature 3 in the sleeve4 vary the magnetic flux acting upon the two coils 7'. The correspondingvoltages thus induced in the coils correspond to the two componentrecordings along the lateral walls of the groove and, uponamplification, are supplied to separate amplifiers and loudspeakers inthe conventional manner.

This general principle of an electromagnetic pick-up may also beembodied in numerous other designs to which the present invention isapplicable. It appears preferable, however, to first explain theinvention with reference to the particular type of pickup exemplified byFIG. 1.

For conveying a realization of the slight dimensions required of theelastic bearing member 5, it should be considered that FIG. 1 is shownon a greatly enlarged scale. The difficulties of mounting the elasticbearing member will be apparent if one takes into account that thehearing has a thickness of only *7 mrn. At the same time, this bearingmember must be soft but, when being assembled with the relatively longsleeve 4, must not suffer the slightest deformation or be subjected totension and assume a precisely defined position. Meeting theserequirements no a greater or lesser extent requires extreme skill and aconsiderable amount of time. It is thus one of the more specific objectsof the present invention to minimize these shortcomings, aside fromatfording additional advantages mentioned hereinafter.

Referring now to FIGS. 2 and 3, it will be noted that according to theinvention a portion 8 of the pole shoes, denoted by 6 in FIG. 1, isdesigned as a separate piece and is seated upon the remaining, fixedpole-shoe portion 11 so as to protrude beyond the fixed ortion. Thisresults in forming intermediate spaces 9 (FIG. 3) in which the annularbearing member 10 of synthetic rubber or the like elastomeric materialis located. Denoted by 12 in FIG. 2 is one of the separating faces uponwhich the adjacent removable pole-shoe portion 8 is closely but slidablyseated. The remainder of the magnetic circuits 7 may correspond to thoseshown in FIG. 1. It will be noted that the cavity formed by the spaces 9has a considerably larger width or diameter than corresponds to thewidth of the etfective pole gap between the pole shoes. Accordingly, thewidth of the elastic bearing member 10 located in the cavity is alsomuch larger than the width of the pole gap.

The elastic hearing member 10 is seated upon the armature 3 to adherethereto by friction and is fixed in position by rings 13 which areeither elastic or cemented to the armature 3. Consequently the bearingmember 10 need be subjected to only little stress for sufiicientfrictional seating. If desired, the bearing member 10 may also becemented or vulcanized upon the armature 3. The periphery of the elasticbearing member 10 abuts against the walls of the cavity 9 to permitpivoting motion of the armature 3 toward all sides under the slightreturn force of the elastic hearing which nevertheless is sufficientlylarge and accessible for convenient handling during assembling work.

The pickup may be made and assembled as follows. The four pole-shoeportions 8 are first joined with each other by a supporting structure'14 of synthetic plastic, aluminum or other non-magnetic material tojointly form a single rigid unit. In this manner, the pole-shoe portions8 are fixed in their positions relative to each other. It is preferableto thus rigidly fasten the removable pole-shoe portions by injectionmolding or embedding them into a body of casting or potting resin shapedas a plugtype structure. The synthetic plastic may be transparent sothat the interior remains visible to facilitate the subsequent mountingof the bearing member 10.

The elastic bearing member 10 is preferably seated upon the armature 3outside of the structure 14 just described. The locality of the bearingmember 10 is approximately at the gravity center of the vibratory systemcomposed of parts 1 to 3, in which position the bearing member 10 isthen fixed to the armature, for example by means of the aboveanentionedrings 13. Thereafter, the entire system of parts 1 to 3 with the bearingmember .10 seated thereupon, is inserted from the right (FIG. 2) intothe hollow cavity 9 (FIG. 3). At this time, the structure 14 with theremovable pole-shoe portions 8 is still separate from the housing 15 ofthe pickup in which the main portion of the magnetic circuits 7 with thefixed pole-shoe portions 11 is mounted.

The cavity 9 forms a generally quadrangular cup space with rounded edgeswhose cross section is apparent from FIG. 3. Of course, the crosssection of this cup space may be given a circular or any other desiredshape. As the stylus system 1 to 3 together with the bearing member 10is being inserted, it is moved to the position shown in FIG. 2. Thisassembling procedure is readily observable because the cavity 9 remainsvisible from the right and the stage at which the bearing member 10 justreaches the cup bottom of the cavity and hence the position shown inFIG. 2, can be observed through the opening 16 through which the styluscarrier 2 emerges. If the structure 14 consists of transparent plastic,the assembling work can be additionally checked by inspection throughthe transparent wall.

It will be apparent that the large dimensions of the bearing member 10permit reliable handling and inserting it in such a manner that it willnot become compressed or otherwise deformed. This virtually eliminatesthe danger of impairing the extremely small reproduction quality byelectricity-distorting deformations of the bearing member as are apt tooccur, on account of its extremely small dimensions, in a pickupaccording to FIG. 1. As a result, the production of a large number ofpickups having uniformly optimal qualities is greatly facilitated.

After the elastic bearing member 10 is inserted into the cavity 9,further fixing of the bearing member is not necessary, as a rule,because the member is kept in position by the above-mentioned frictionalconnection with the armature. This is aided by the fact that the weightsof the individual parts are very small so that minute pressures of thebearing member against the walls of the hollow space 9 will sufiice tosecure a sufficient frictional seating. During operation of the pickup,the front faces of the fixed pole-shoe portions 11 confine the elasticbearing member 10 and thus also contribute to securing it in the correctposition. As mentioned, however, the bearing member may be additionallyfastened to the armature by cementing, elastic rings .or the like.

As further shown in FIG. 2, a cup-shaped sleeve 17 of non-magneticmaterial has its open side abut against the elastic bearing member 10,the other side 18 of the sleeve being closed. The cup-shaped sleevereceives a portion of the armature 3 and is filled with a damping medium19, such as silicone grease, which surrounds the enclosed portion of thearmature. The sleeve 17 is further shown to have its opening surroundedby an outwardly directed flange 20 at which the sleeve is firmlyconnected with the pole-shoe portions 8, thus forming part of theexchangeable assembly unit.

This affords several further advantages. In the first place, the elasticbearing member 10 is positionally fixed by the flange 20. The flange 20engages for example a groove 21 of the removable pole-shoe portions 8and/or of the unit 14 and, on the other hand, is in lateral engagementwith the elastic bearing member 10. As a result, the elastic bearingmember 10 is confined on both sides and consequently need have no morethan touching or guiding engagement at its outer periphery with the, forexample, cylindrical circumference of the hollow space 9, without beingrequired to exert pressure upon the armature to effect frictionalseating. Another advantage is the fact that the right-hand end of thearmature 3 is protected. The armature can neither be touched nor damagedduring assembling, shipping or exchanging of the assembly unit. Theseadvantages are obtained even if the cup-shaped sleeve 17 is not filledwith a damping medium 19. The provision of this medium, however,improves the reproduction quality by securing a periodic oscillation ofthe system 1 to 3. A similar damping effect may be achieved, at leastpartially, by the elastic bearing member itself. However, providing forseparate damping with the aid of a medium as shown at 19 makes itunnecessary to select the dimensions or the material of the elasticbearing member with a view to obtaining any damping effect.

The assembly unit on structure 14 is joined with the pickup housing 15by plugging the unit into an outwardly open recess 23 of the housing.This recess may be given various shapes, for example a predominantlysquare cross section as shown in FIG. 3, although a circular crosssection is likewise applicable, for example. It is preferable to providethe unit 14 with guiding parts, such as a guiding nose 240 or the like,which are spaced farther away from the armature 3 than the pole-shoeportions 8 and which determine the position of the exchangeable assemblyunit relative to the housing 15 of the pickup. By such means, theexchangeable unit is constrainedly guided to its correct position and,when fully inserted, is fixed in this position relative to the housingof the pickup.

When the exchangeable unit is being plugged into the pickup housing, theremovable pole-shoe portions 8 fit snugly over the fixed pole-shoeportions 11 along which they slide to the proper position shown in FIG.2. The mutually sliding pole-shoe faces are denoted by 24 and 25. Themutual engagement may be such that when the removable assembly unit isbeing plugged into proper position, the pole-shoe portions 8, as theyadvance along the fixed pole-shoe portions, will slightly press upon thelatter and thus improve the magnetic engagement. It is preferable,therefore, to make the legs of the magnetic circuits 7, or partsthereof, somewhat resilient, for example in the leg portions adjacent tothe pole shoes. This affords a particularly intimate mechanical andmagnetical junction of the exchangeable pole-shoe portions with thefixed pole-shoe portions. In addition, the sleeve 17 likewise may bemade resilient so that it abuts with resilient force against thepole-shoe portions 11. This may be done, for example, by having thecylindrical shape of the sleeve bulge somewhat outwardly so that whenthe sleeve is being pressed together by the pole-shoe portions 11, thesleeve will be elastically deformed to the illustratedstraight-cylindrical shape.

The magnetic circuit structures 7 may be mounted in any desired mannerin the housing 15 of the pickup. It is particularly simple to embedthese magnetic components, including such accessories as the coils andtheir terminals, in casting or potting resin which coalesces with thematerial of the pickup housing or is filled into a recess provided forthis purpose in the housing.

It is further preferable to provide the supporting structure 14 of theexchangeable assembly unit with a grip 26 or a protective cover 27 forthe stylus carrier 2, or both, as is the case with the embodimentillustrated in FIG. 2. The grip or handle 26 as well as the protectivehood 27 above the stylus carrier may consist of a single piece with themounting structure 14 or may be mechanically connected thereto. Thisresults in a large and handy unit, despite the fact that thereproductively active components proper have minute dimensions. Theentire assembly unit can be easily and rapidly exchanged by a layman. Inaddition, the invention combines the advantages afforded by a sleeve asshown at 4 in FIG. 1 with the possibilities of improving thereproduction heretofore afforded only with pickups whose stylus assemblyis not exchangeable. This will be understood from the following.

It will be recognized from FIG. 1 that the wall thickness of the sleeve4 in a pickup of the known type occupies an essential share of thenarrow air gap. It is of advantage to keep the air gap narrow but topreserve the dessired ease of exchangeability. With the known type ofpickup, however, an attempt at reducing the air gap is limited not onlyby the required wall thickness of the sleeve but also by the fact thatthe elastic bearing member 5 must have a minimum thickness in order topermit large-scale assembling and secure the desired mobility andcompliance of the stylus point 1.

By comparison with FIG. 2 it will be recognized that by virtue of theinvention these limitations are largely eliminated. The air gap can bekept very narrow because the wall thickness of the sleeve 17 is nottroublesome as it does not affect the size of the bearing member 10 andsince the armature movements are very small. The reduction of the gapwidth has the consequence that the available output voltage is higherthan heretofore. Furthermore, any spurious fields, for example from thedrive motor of the phonograph, can have only a greatly reducedinterfering influence. Both effects improve the signal-tonoise ratio ofthe pickup. If desired, this improvement may also be utilized forreducing the dimensions of the armature. This, in turn, affords reducingthe tracking force and improving the vertical and lateral compliance,

7 thus imposing less wear upon the record discs and making finer detailsof the recordings audible for an increased number of repetitions.

Although in the foregoing the novel features and ad vantages of theinvention have been described in comparison with the known pickup shownin FIG. 1, the invention is not limited to systems of this particularkind. For example, it may be applied equally well to variable-reluctancepickups in which a permanent magnet is associated with the stationaryportion of the magnetic circuit or circuits and the vibratorily mountedarmature consists of magnetically soft material. The invention isfurther not limited to the reproduction of stereophonic recordings. Forexample, the pickup portion shown in FIG. 2 having a single magneticcircuit may serve for reproducing only one component of a magneticcomponent or for reproducing a monaural recording. For the purpose ofmore lucid illustration, the stylus point 1 is shown to have its axis inthe plane of illustration in which the armature 3 is pivotally movable.This design would be suitable for the reproduction of depth recordings.If the magnetic system is turned 90, the system would be suitable forreproduction of lateral recordings. If the system comprises two magneticcircuits 90 displaced from each other according to FIG. 1, the pickup issuitable for twocomponent recordings such as stercophonic records. Sinceit is not customary to use depth and lateral components for suchpurposes but to have the two component recordings located on therespective two lateral walls of the record groove, the stylus axis forstereophonic recordings of the latter kind must be 45 displaced fromeach of the axes of mutual spacing between the two poles of eachmagnetic circuit, this being shown in FIG. 3.

The removable pole-shoe portions 8 may be joined with the supportingstructure 14 by first embedding these poleshoe portions in theunfinished state within the nonmagnetic material, for example aluminum,which is to form a block-shaped supporting structure. During casting ofthe embedding material the pole-shoe portions 8 are held in the properpositions relative to each other and as required for subsequentcooperation with the armature 3 and the fixed pole-shoe portions 11. Theresulting solid block is thereafter machined so that the pole-shoeportions 8 obtain at their respective ends the correct junction faces 12for engagement with the fixed pole-shoe portions and at their other endsthe correct pole faces 28 relative to the armature 3. In this manner, ahighly accurate position of the pole-shoe portions 8 and 11 as well as asatisfactory stability is achieved together with extremely few specimendifferences in large-quantity production.

The embodiment illustrated in FIGS. 4, 5 and 6 differs from the pickupaccording to FIGS. 2 and 3 mainly in that the supporting structure forthe removable pole-shoe portions is designed as an entity in which theremovable pole-shoe portions are positioned, and which constitutes asub-assembly inserted into a recess of a plug portion of theexchangeable armature-stylus assembly. This affords more freedom in thedesign of the hollow space and the removable pole-shoe portions. Forexample, the size of the elastic bearing member 10 can be still furtherincreased in this manner. Thus, a comparison of FIG. 4 with FIG. 2 showsthat the diameter of the rang-shaped elastic bearing member 10 in FIG. 4is still larger than that of the corresponding member in FIG. 2.

A further improvement is obtained by providing the removable unit withmeans for the constrained guidance of the fixed plesh0e portions whenthe removable assembly is being plugged into the pickup housing, thusfurther facilitating an exchange of the removable assembly by laymen.

The supporting structure 29 of the subassernbly shown in FIGS. 4 and hasa generally cylindrical shape and is hollow. The interior is open at oneside 37 for mounting the armature 3. The bottom 31 is provided withopenings 32 shaped in accordance with the cross section of the fixedpole-shoe portions to provide for constrained guidance of these portions11. The peripheral surface of the structure 29 has radially directedslots for inserting the removable pole-shoe portions 30. Thisfacilitates assembling the armature bearing as well as the armature andalso protects the armature in the assembled condition.

A tubular member 33 forming an integral piece of ma terial with thehandle or grip 26 is positioned over the cylindrical supporting unit 29.A radially extending nose 38 of unit 29 engages a longitudinal groove(not illustrated) of the tubular part 33 to secure both in the properposition and against relative rotation. This is advisable if both partshave a circular cross section. If the cross section differs from thecircular shape, a mutual positioning engagement is not necessary butoften advantageous. The handle structure 26 facilitates exchanging theentire assembly and also protects the stylus carrier 2, aside fromfirmly holding the pole-shoe portions 30 in their respective slots.

The illustrated pole-shoe portions 30 have approximately the shape of aU of which one leg 34 enters into snug contact with the adjacent fixedpole-shoe portion 11. This affords providing the pickup with theabove-mentioned bearing member 10 of very large diameter, because thebearing member may be mounted in the bight space between the legs of theU-shaped pole-shoe portions 30.

It is further preferable to make the leg 34 shorter by the thickness ofthe fixed pole-shoe portion 11 than the other leg of the U-shapedpole-shoe portion 30. With such a design, the plugged-in pole-shoeportion 30 is supported upon the end of the fixed pole-shoe portion 11.The other side of the removable pole-shoe portion 30 is supported byhaving a nose 35 resting upon an annular shoulder 36 of the supportingstructure 29. As a consequence, the full opening 37 of the hollowpot-shaped unit 29 remains available for mounting the stylus system 1 to3 including the elastic bearing member 10, while nevertheless preservingan accurate positioning of the poleshoe portions 30.

Similar to the embodiment of FIG. 2, the pickup shown in FIG. 4comprises a sleeve 17 adjacent to the elastic bearing member 10.However, the sleeve 17 according to FIG. 4 has a radial flange 20engaged by a cover 39. The flange and the cover jointly enclose thebearing member 10 on all sides, thus fully protecting the bearingmember. FIG. 6 shows the stylus system including the thus encapsulatedarmature and bearing member.

The cup portion of the sleeve 17 is inserted into a bore of thesupporting unit 29 in the direction of the arrow indicated in FIG. 5.When thereafter the poleshoe portions 30 are being inserted in radialdirection through the slots, the structure 29 then being held fast, forexample manually, the flange 20 and the cover 39 afford an additionalguidance for the pole-shoe portions 30 which may be positioned likeclamps over the flange and cover on sleeve 17, so that the assemblingwork reuires no particular skill. Furthermore, the flange 20 and thecover 39 may have some resilience so as to yield during assembling. Forthis purpose the flange 20 and the cover 39 may be given a somewhatbulging shape. Then each pole-shoe portion 30, when being inserted intothe unit 29, presses the flange 20 and the cover 39 to the respectiveplanar shapes. Another way of providing for resiliency is to cut a slitinto the cylindrical margin of the flange 20 to produce a resilienttongue 41 according to FIG. 6. Still another or additional way is toposition a broad rubber ring upon the peripheral outer sur face of theunit 29.

Pickups according to the invention may be modified in various respects.Thus the embodiments shown in FIGS. 7, 8 and 9 exemplify different otherways of separating the removable pole-shoe portions from the remainingfixed portions and giving the removable portions respectively differentshapes, the pickup in each case being assumed to correspond otherwise tothe one shown in FIG. 1, for example.

The embodiment illustrated in FIGS. 2 and 3 may be looked upon as beingcharacterized by the fact that the hollow space for accommodating theflexible bearing member for the armature is formed by the inner lateralfaces of the removable and angularly shaped pole-shoe portions 8, on theone hand, and the front faces of the remaining, fixed pole-shoe portions11, on the other hand. As shown, the elastic bear-ing member may rest onall sides against the peripheral wall of the hollow space thusconstituted. However, the invention also contemplates pickup designs inwhich the bearing member abuts only against those wall portions of thehollow space that are most remote from the armature 3. For example, thebearing member 10 may be made somewhat narrower in width than the hollowspace so that air gaps remain along both lateral walls. The same purposeis served by a pickup in which the shape of the hollow space departsfrom that of the bearing member so that the bearing member is bracedessentially only against the wall most remote from the armature in thehollow space.

The embodiment shown in FIG. 7 is of the latter type. That is, a gapspace 44 is left between the lateral sides 42 of the elastic bearingmember 10 and those wall components 43 of the hollow space that face thebearing member. While the hollow space as well as the elastic hearingmay be given various shapes, they are shown in FIG. 7 to leave awedge-shaped interspace 44. This requires giving the walls of the hollowspace and consequently the respective surface areas of the pole-shoeportions an inclined direction as compared with that shown in FIG. 2.However, the same result is also obtainable by giving the lateral sides42 of the bearing member 10 an inclined puition, resulting in anoutwardly tapering cross section of the bearing member. By virtue ofsuch features, the bearing member 10' abuts only against: the wallportions 45 most remote from the armature 3. This results in a higherdegree of softness and consequently a very slight return force of thebearing member even if its dimensions are relatively small.

Various modifications are also applicable with respect to the shape andarrangement of the planes of separation between the removable and fixedpole-shoe portions. Thus, according to FIG. 8, the separation surface 46lies flush with the adjacent lateral side of the flexible hearing member10. This further improves the accessibility of the bearing member duringassembling and facilitates checking the member for proper seating.

FIG. 9 exemplifies another way of shaping the removable pole-shoeportions as well as a different shape and arrangement of the separationsurface. While in the embodiments so far described the separation faceextends either perpendicularly to the plugging direction of theexchangeable armature-stylus assembly or parallel to that direction, theseparation surface in the pickup according to FIG. 9 extends in part ata different angle, for example 45, to the just-mentioned directions.This portion of the separating face is denoted by 48, a residual portion49 extending in the plugging direction of the exchangeable assembly.

It will be noted that in an embodiment of the type shown in FIG. 9, thepossibility of giving the elastic bearing member 10 a larger diameterthan corresponds to the width of the gap between the pole shoes is muchmore limited than with embodiments according to FIGS. 2 to 8. On theother hand, a pickup according to FIG. 9 may be obtained from thecomponents of a known pickup according to FIG. 1 simply by providing theoriginally undivided pole shoe with a recess 50 (FIG. 9) for receivingthe elastic bearing member 10, and separating the pole-shoe portion 8 inthe illustrated manner from the rest of the pole s oe. This permits amanufacturer of the original pickups to employ a large number of alreadyavailable parts in the production of improved pickups according to theinvention.

It will be apparent from the variety of embodiments illustrated anddescribed herein, that the invention affords numerous modifications. Forexample, combinations of the different features described in theforegoing with reference to respectively different embodiments arereadily applicable in a single pickup. Thus individual arrangements anddesigns of the separation faces may be combined with different shapes ofthe pole-shoe portions. Among these is a design in which the removablepole-shoe portions 8 are straight and the fixed pole-shoe portions 11are curved or angular, thus constituting essentially an inversion ofsuch pole-shoe portions 8 and 11 as shown in FIG. 2. To those skilled inthe art, it will be obvious therefore that our invention may be givenembodiments other than particularly described herein, without departingfrom the essential features of our invention and within the scope of theclaims annexed hereto.

We claim:

1. An electromagnetic pickup for phonograph records, comprising amagnetic circuit provided with coil means and having at least one pairof pole shoes spaced from each other to form a pole gap and a vibratoryarmature in said gap, said armature extending in length substantiallyparallel to and spaced from said pole shoes and having a length which isless than that of any of said pole shoes, each of said pole shoes beingsubdivided into a fixed portion and a removable end portion at said gap,said removable end portion engaging said fixed portion and protrudingtherefrom, an exchangeable assembly comprising said armature and astylus carrier secured to said armature with a stylus mounted on saidcarrier, said armature and said stylus carrier extending colinearly,each of said removable pole shoe portions being part of saidexchangeable assembly and forming, when engaging one of said respectivefixed portions and conjointly therewith, an intermediate space betweenthe removable end portion and the corresponding fixed portion laterallyof and extending to and opening on said armature, two opposite ones ofsaid spaces having conjointly with said pole gap 2. larger width thansaid pole gap only, and an elastic bearing member surrounding saidarmature and joined therewith, said member being mounted in said space.

2. A pickup as claimed in claim 1, wherein said exchangeable assemblycomprises a structure of non-magnetic material fixedly interconnectingsaid pole-shoe end portions and forming a cavity which includes saidintermediate spaces.

3. A pickup as claimed in claim 1, wherein said exchangeable assemblycomprises a structure of non-magnetic material fixedly interconnectingsaid poleshoe end portions and forming a cavity which includes saidintermediate spaces, said elastic bearing member being located in saidcavity and having a shape departing from that of said cavity to formannular interstices on the respective axial sides of said bearingmember, said bearing member being in pressure contact with said cavitysubstantially only at the perimetric surface.

4. A pickup as claimed in claim 1, wherein said poleshoe end portionshave angular shape, and said intermediate spaces are formed by the innerlateral faces of said end portions and the respective adjacent frontfaces of said fixed pole-shoe portions.

5. A pickup as claimed in claim 1, wherein said poleshoe end portionshave substantially L-shape and have the inner side of one of the L-legsslidingly engageable with one of said respective fixed portions on thelateral side facing away from said gap, said intermediate space beinglocated between said inner side of said L-leg and the adjacent end faceof said fixed portion.

6. A pickup as claimer in claim 1, wherein said bearing members has theshape of an annular flat disc, and the plane of division between saidfixcd and removable poleshoe portions is flush with one flat side ofsaid disc.

7. A pickup as claimed in claim 1, wherein said fixed and removablepole-shoe portions have conjointly the shape of a straight bar, saidintermediate space forming a lateral recess in one side of said barshape, and the division between said fixed and removable portionsextending from the opposite side of said bar shape into said recess.

8. A pickup as claimed in claim 1, wherein said fixed pole-shoe portionsof said magnetic circuit are resiliently displaceable toward each other.

9. A pickup as claimed in claim 1, wherein said removable pole-shoeportions have lateral inner faces slidably engageable in the insertingdirection of said exchangeable assembly with lateral outer faces of saidrespective fixed pole-shoe portions.

10. A pickup as claimed in claim 1, wherein said hearing member has asubstantially annular shape and an outer periphery in radial pressureengagement with said pole-shoe end portions.

11. A pickup as claimed in claim 10, wherein said bearing member andsaid cavity are in mutual pressure engagement at substantially only thecavity wall portions most remote from said armature.

12. A pickup as claimed in claim 1, wherein said removable pole-shoeportions have substantially U-shape, one leg of the U-shape beingengageable with one of said respective fixed pole-shoe portions, andsaid intermediate space is located in the bight of said U-shape.

13. A pickup as claimed in claim 12, wherein said one leg is shorterthan the other by the thickness of said fixed pole-shoe portion andengages said fixed portion on the lateral side of the latter facing awayfrom said pole gap.

14. An electromagnetic pickup for phonograph records, comprising ahousing having an exteriorly accessible recess, magnetic circuit meansmounted in said housing and having fixed spacedapart pole-shoe portionsprotruding into said recess, an exchangeable armature-stylus assemblyhaving a rigid supporting structure, pole-shoe end portions fixedlymounted in said structure in mutually spaced relation and insertableinto said recess for engagement with said respective fixed pole-shoeportions, said structure having between the end portions of saidpole-shoe portions mounted in said housing and the end portions of saidpole-shoe portions mounted in said structure a cavity whose width islarger than the spacing between said pole-shoe portions, an annularbearing member of elastomeric material seated in said cavity, a magneticarmature coaxially joined with said bearing member and extending axiallyaway therefrom in opposite directions between said fixed pole-shoeportions and between said end portions respectively, said armatureextending in length substantially parallel to and spaced from said poleshoes and having a length which is less than that of any of said poleshoes, said cavity extending to and opening on said armature, and stylusmeans fastened to said armature and extending colinearly therewith, saidassem bly being insertable and removable as a whole relative to saidhousing.

15. A pickup as claimed in claim 14, wherein said supporting structureof said exchangeable assembly consists of synthetic plastic and forms aplug removably insertable into said recess of said housing.

16. A pickup as claimed in claim 14, wherein said supporting structurecomprises an integral handle portion to be gripped manually forexchanging said assembly, and said structure has an integral protectivehood portion which covers said stylus means from above.

17. A pickup as claimed in claim 14, wherein said assembly comprises anenclosure having a tubular plug portion insertable into said recess,said supporting structure being disposed in said plug portion and havingradial slots into which said respective pole-shoe end portions areinserted, said slots being adjacent to the inner surface of said tubularportion so that said end portions are held in said slots by said tubularportion.

18. A pickup as claimed in claim 17, wherein said supporting structureforms a cylindrical cup, said slots extending through the cylindricalwall of said cup, the bottom of said cup having holes to be traversed bysaid fixed pole-shoe portions, and said stylus means extending out ofthe cup opening of said structure.

19. An electromagnetic pickup for phonograph records, comprising amagnetic circuit provided with coil means and having at least one pairof pole shoes spaced from each other to form a pole gap and a vibratoryarmature in said gap, each of said pole shoes being subdivided into afixed portion and a removable end portion engaging said fixed portionand protruding therefrom; a cup-shaped sleeve of non-magnetic materialhaving a transverse flange extending about the cup opening, said sleeveforming an envelope around said armature and being filled with dampingmedium;

an exchangeable assembly comprising said armature and a stylus carriersecured to said armature with a stylus mounted on said carrier, each ofsaid removable pole-shoe portions being part of said exchangeableassembly and forming, when engaging one of said respective fixedportions and conjointly therewith, an intermediate space laterally ofsaid armature, two opposite ones of said spaces having conjointly alarger with than said pole gap; and

an elastic bearing member surrounding said armature and joinedtherewith, said member being mounted in said spaces, the flange of saidcup-shaped sleeve being adjacent to one side of said bearing member andattached to said assembly.

20. A pickup as claimed in claim '19, wherein the flange of said sleeveis fastened to said pole-shoe end portions.

21. A pickup as claimed in claim 19, further comprising a non-magneticcover disposed on the other side of said bearing member, said flange andsaid cover forming together a capsule enclosing said bearing member.

22. A pickup as claimed in claim 21, wherein said flange and cover areof elastically deformable sheet material to act as radially compressiblesprings.

References Cited UNITED STATES PATENTS 3,077,521 2/1963 Ahrens l79l00.4l3,067,295 10/1964 Stanton 179l00.41 3,299,219 1/1967 Madsen 179l0().41

BERNARD KONICK, Primary Examiner. L. H, HILL, R. F. CARDllLO, AssistantExaminers.

